The field of the invention is cables containing telecommunications elements such as optical fibers. Light waveguides will be referred to throughout as optical fibers. Such optical fibers normally include at least one protective outer coating.
Siecor's well-known Mini Bundle loose tube optical fiber cable contains a steel or dielectric central member having a plastic overcoat, a layer of buffer tubes stranded with reverse alternating lay around the central member, a viscous filling compound and a plurality of optical fibers loosely contained in each buffer tube, a layer of aramid fibers surrounding the buffer tubes, a viscous flooding compound filling spaces around the buffer tubes, and an outer sheath with an optional steel tape armor. Optical fibers within the buffer tubes have intended excess fiber length. Twisted pair electrical conductors inserted side-by-side with the buffer tubes have been provided as an optional feature. However, such insertion of the electrical conductors may cause the outer diameter of the cable to be increased.
Barnes, U.K. patent application GB 2,215,081, published Sep. 13, 1989, discloses a central strength member surrounded by a layer of plastic tubes stranded thereabout. Each plastic tube contains a stack of optical ribbons and is filled with a viscous filling compound. The layer of plastic tubes is surrounded by a paper tape and an outer plastic sheath, and a viscous flooding compound fills the cable interstices between the plastic tubes and the paper tape. The length of the optical ribbons is similar to the length of the plastic tubes, although there may be a slight excess length.
Another cable including a central member surrounded by tubes each holding a stack of optical ribbons and including a flooding compound is U.S. Pat. Nos. 5,229,851. This cable contains a viscous flooding compound, and the optical ribbons have an intended length which is greater than that of the tubes containing the optical ribbons.
Viscous flooding compounds used in the prior art cables discussed above between the buffer tubes and the outer sheath are messy when the cable must be entered in midspan to reroute or connectorize individual optical fibers or ribbons to reconfigure the network. Other means to protect the optical fibers from contact with moisture have been proposed for use in optical fiber cables. Those alternate means include tapes, yarns, and powders including water-absorbent materials therein.